Did dinosaurs really roar? Probably not, say scientists.

New research suggests that some dinosaurs may have sounded more like ostriches than ferocious monsters. 

Museum of the Rockies/AP
This 2001 photo shows a bronze cast of the Tyrannosaurus rex skeleton known as the Wankel T.rex, in front of the Museum of the Rockies at Montana State University in Bozeman, Mont. Scientists say that rather than roaring, dinosaurs likely made cooing or mumbling sounds similar to those made by pigeons or ostriches.

New research on the vocalizations of dinosaurs may make "Jurassic Park" seem a little less scary.

In a study published in the journal Evolution, scientists say that rather than roaring, some dinosaurs likely made cooing or mumbling sounds similar to those made by pigeons or ostriches. 

Today's birds make these low-pitched sounds, known as "closed-mouth vocalizations," by pushing air that powers sound production into a pouch in their esophagus, instead of exhaling it back out of their beaks. The sound is emitted through the skin in the neck area, typically while trying to attract mates or defending territory.

There is no direct fossil evidence yet to tell us what dinosaurs sounded like but the new research on the evolution of such vocalizations offers strong clues.

"To make any kind of sense of what nonavian dinosaurs sounded like, we need to understand how living birds vocalize," Julia Clarke, a professor at the University of Texas's Jackson School of Geosciences and co-author of the study, said in a press release. "This makes for a very different Jurassic world. Not only were dinosaurs feathered, but they may have had bulging necks and made booming, closed-mouth sounds."

Using a statistical approach, Dr. Clarke and her team analyzed the distribution of closed-mouth vocalization among archosaurs, a group that includes birds, crocodiles, and dinosaurs. They discovered that 52 out of 208 investigated bird species have the vocal ability to make such sounds, and that only animals with a relatively large body size (about the size of a dove or larger) use the behavior.

"Looking at the distribution of closed-mouth vocalization in birds that are alive today could tell us how dinosaurs vocalized," said study co-author Chad Eliason, a postdoctoral researcher at the Jackson School. "Our results show that closed-mouth vocalization has evolved at least 16 times in archosaurs."

Whether the ancestors of modern archosaurs actually used closed-mouth vocalization is still unknown. However, the fact that it's used by both birds and crocodiles, the two surviving groups of archosaurs, suggests that the behavior can exist in a wide range of archosaur species, says Tobias Riede, a physiology professor at Illinois's Midwestern University and first author of the study.

Furthermore, many dinosaurs had the large body sizes required to produce such sounds. 

"A cool thing about this work is the demonstration that closed-mouth behavior evolved many times," Dr. Riede said in the release. "That suggests it can emerge fairly easily and be incorporated into mating displays."

The team's next move will be to integrate information from fossils, experimental physiology, gene expression, and sound modeling into their research.

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